In many scaffolds a work cage is mounted on a columnar support structure which is usually telescopic in nature so as to be compact for mobility and storage and vertically extendible, manually, pneumatically, or hydraulically, so as to permit the workman to reach substantial ceiling heights.
Scaffolds of this type require a large base support area to provide stability to the scaffold when in use. The larger base support area can be obtained by using a large permanent base structure, but this will prevent the scaffold from being moved from place to place through restricted passageways. To overcome this deficiency, outrigger members are in general use, the outriggers being retractable for movement of the scaffold and extendible when the scaffold is to be used. However, since setting of the outriggers requires some degree of effort on the part of the workman, there may be instances in which a careless workman may fail to set the outriggers.
As a consequence, it is desired to provide a scaffold with such a relatively small base structure in its mobile mode that it will be plainly apparent that the outrigger members attached to the scaffold must be set in their operative position before the workman may safely ascend the scaffold.
Mobile scaffolds are conventionally mounted on lockable casters to permit the scaffolds to be moved from place to place when the casters are unlocked and to permit the scaffold to be immobilized when the casters are locked. However, some type of work may require frequent movement of the scaffold at a work site, as for example, when ceiling lights are replaced. In such situations, and in complete disregard of manufacturer's recommendation and safety regulations, the workman may deliberately choose to leave the casters unlocked. By so doing, he is then able to mount to and stay in the elevated cage and move the scaffold along the floor by grasping the ceiling or wall and exerting a horizontal pull to roll the scaffold on its unlocked casters. Or else, he may have another workman at the base of the scaffold push the scaffold along the floor. In either case, if one or more of the casters encounters an obstacle on the floor, there is a possibility that the scaffold could be tipped over.
As a consequence, in pedestal type scaffolds which are equipped with casters for movement of the scaffold, there is a definite advantage in providing an arrangement wherein the scaffold cannot be moved when a workman is on the scaffold.